Method of running a synchronous motor.



A. R. BULLOCK.

METHOD OF RUNNING A SYNCHRONOUS MOTOR. APPLICNTIQN F |LED AUG. 2 .-1912. RENEWED SEPT. 20. 1916.

1,223,472. Patented Apr. 24, 1917.

li/ flze 666 6 j: 1/671 2 0 I.

(IT/M UNITED STATES PATENT OFFICE.

ARTHUR R. BULLOCK, or CLEVELAND, OHIO, ASSIGNOR To THE ERIE ooIL COMPANY,

- or CLEVELAND, care, A CORPORATION or OHIO.

METHOD OF RUNNING A SYNCHRONOUS MOTOR.

Specification of Letters Patent.

Patented Apr. 24, 1917.

Application filed August 2, 1912, Serial No. 713,016. Renewed September 20, 1916. Serial No. 121,311.

To all whom it may concern Be it known that I, ARTHUR R. BULLOCK, a citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented a certain new and useful Improvement in Methods of Rum ning a Synchronous Motor, of which the following is a full, clear, and exact description.

This invention relates to synchronous motors, or what may perhaps more properly be termed a method of operating synchronous motors.

In using a synchronous motor in connection with certain forms of alternating current apparatus, it is necessary that the motor run in absolute rotative position synchronism with the generator supplying the alternating current, and further, that the syn-.

chronous motor shall respond very readily to any changes in the angular velocity of the generator.

As one instance of such an alternating current machine as mentioned above, I would cite a mechanical converting device,.- that is to say, a device comprising a commutator with se ents thereon, arranged in groups,'to whlch an alternating current may be fed, and which will deliver a direct current. Such machines must have the commutator thereof rotated by a motor rotating in precise synchronism with the generator from which the alternating current is generated,that is to say, the rotors of the motor and generator must rotate as nearly in absolute step as it is possible to make them,

and moreover, the commutator must be rothat the current waves passing through the commutator and through the motor must be absolutely in step.

I have found that this result may be ac complished by running the synchronous motor with the field excitation much below that which is the normal excitation, or in other words, running the motor so that the fields are excited only suflicient to prevent the motor from falling out of step.

The motor is usually started in the usual way, with the field excitation of the'normal amount designed for the motor. As a concrete illustration, we may take .as an example, a one-half horse power syn In running such a motor in the manner heretofore indicated, I would start the motor by using the normal field excitation,-that is to say 150 watts, and as soon as the motor was running synchronously and at proper speed, then the field excitation would be reduced to approximately 20 watts, in which condition, the motor would operate at its designed capacity, and would run absolutely free from any hunting.

Under the condition described, it has been found that the motor keeps in absolute synchronism with. the generator Whose alternating current it is using, and further, that the motor responds very quickly to any changes in frequency conditions, which may occur on the line. Y

-So close is the regulation, I have found, that a given point upon the rotor of the motor does not vary of an inch on a 7 inch radius, from a similar point upon the generator rotor.

In the figure of the drawing, there is shown diagrammatically one'way in which a synchronous m'otor may be operated in the manner described.

The motor frame is shown at 'A, andthe pole pieces are indicated at B, B, B and B These pole pieces are wound so as to secure the proper field excitation, as indicated in the drawing, and the pole pieces on one side of .the machinemay be wound and connected in one circuit, while the pole pieces upon the other side of the machine, are wound in the opposite direction, and connected in a different circuit. The terminals of both circuits, may be connected with suitable binding posts, indicated at C, D, E and F. These binding posts will be connected with a double throw switch, the bindin post C being connected with the point of the switch, while the binding post F is connect- 1) ed with the point H of the switch. The binding post E will be connected with the point .I of the switch, while the binding.

the windings upon the pole pieces B, B are.

in parallel with the windings upon the pole pieces B and B Under such conditions, the current passing through the respective windings, will produce the normal full field excitation. This will be the condition under which the motor will be started.

lVhen the motor is running at its proper speed, and in synchronism with the alternating current, the knife blades M will be thrown into contact with the points K and L. This change may be quickly made, and will not throw the motor out of step.

With the blades M contacting the points K and L, the windings upon the'pole pieces B, B, B and B will be in series. In this manner, resistance will be introduced into the circuit producing the field excitation, and this resistance will cut down the flow of current through the windings, resulting in less field excitation than would be the case in the first condition described.

The windings upon the pole pieces may be so proportioned as to produce. the proper field excitation under the starting condition, and the running condition.

The. particular windin of the pole pieces just described is to be ta en merely by way of illustration, and as in no way limitng the invention, I

Having thus described my invention, what I claim is:

1. The method of operating a synchronous motor when the motoris running in synchronism, which consists in supplying the field windings of the motor with an amount of current which is just sufiicient to keep the motor from falling out of step, regardless of the power factor of the exciting circuit.

2. The method of. operating a synchronous 1notor, which consists in starting the motor with the normal field excitation and when the motor is running at proper speed, and in sync-hronisni, reducing the field excitation considerably below the normal field excitation and continuously running the motor with the fields under excited, regardless of the change of power factor of the exciting circuit.

In testimony whereof, I hereunto affix my signature in the presence of two witnesses.

ARTHUR R. BULLOCK.

Witnesses:

A. J. HUDSON, E. M. FREEMAN. 

